REPORT 'New Frontiers of Taste' Vol. 1

June 2005

  • - Professor Edmund T. Rolls

    How Umami Tantalizes Your Taste Buds

    In our July issue, we brought you details of the 'New Frontiers of Taste' event, held as part of the Cheltenham Science Festival on 9th June, which brought together an eclectic mix of guest speakers, each of whom was an expert in his or her taste-related field. Their mission was to approach the subject of taste from a variety of scientific and practical perspectives, and in particular to provide the audience with a deeper understanding of umami. (To read the full article, click here)

    Professor Rolls was billed as someone who would take the audience on a 'journey through the science of pleasure', and at the end of his 10 minute talk on the subject, the Cheltenham audience can certainly be said to have travelled a long way towards an understanding of how taste affects our body, and in particular why umami has a unique effect on both our taste buds and our brains.

    While some of those present, such as fellow panellist Stefan Gates, may have harboured some doubts about the existence of umami as a distinct taste, Professor Rolls emphatically stated that "there IS a fifth taste."

    Natural Taste Sensation

    One of the most basic questions about umami is of course, 'what is it?', and Professor Rolls introduced the audience to the key substances responsible for the taste, namely glutamate, which occurs naturally in a variety of foods including vegetables such as tomatoes and mushrooms, and inosinate, found mainly in meat and fish. Possibly in response to people who may only associate umami with Monosodium Glutamate (MSG), the compound which contains glutamate in its purest form, Professor Rolls said, "I would like to emphasise that umami is a natural ingredient in many foods."

    There was a small murmur of agreement throughout the audience when someone brought up the subject of 'Chinese Restaurant Syndrome' - the phenomenon where some people feel unwell after a visit to certain oriental eateries, and blame it on an excessive amount of MSG being sprinkled onto food to make it more appetising. Professor Rolls commented that the published evidence did not support this view.

    The most revealing part of Professor Rolls' talk was his explanation of exactly how taste in general, and umami in particular, affects us. That Professor Rolls is eminently qualified to explain this is not in doubt - as well as being a neuroscientist specialising in taste, he has recently authored a book called 'Emotion Explained', published by Oxford University Press in 2005, exploring why we find certain tastes so pleasurable.

    He explained that there are taste receptors on our tongue that recognize umami, and that these send messages to two distinct areas in the brain - the primary taste cortex, and the orbitofrontal cortex. The orbitofrontal cortex, the cortex just above the eyes, contains the secondary taste cortex. He described how umami, and more specifically glutamate, affects these cortical taste areas of the brain.

    "Some brain cells increase their 'firing rate' to the taste of glutamate, but not to other tastes, and this is part of the evidence that umami is a fifth taste," explained the Professor.

    Umami Really Whets Your Appetite

    Umami is important not only because it imparts a delicious flavour which makes food more pleasurable, however. As Professor Rolls went on to explore, the umami taste, by making food pleasant, can play an important role in how our appetites work. Further, hunger influences how pleasant umami tastes. In other words, we are programmed to find foods with the umami taste appetising when we are hungry, but when we are full we do not want to eat them nearly so much. Another important factor in appetite is the fact that after we have eaten one food, it taste less pleasant, but other foods remain pleasant to taste.

    "This phenomenon", explained the Professor, "is the most important factor that decides how much you eat at a meal. This has a lot of implications if you are trying to lose weight, and lots of implications if you are trying to boost someone's food intake. We call it sensory specific satiety."

    This finding was illustrated by an experiment carried out by the Professor where he monitored activity in the orbitofrontal cortex of a number of people, whilst they consumed some tomato juice, a savoury food rich in umami. "As they drank the tomato juice to satiety", explained the Professor, "the pleasantness rating went down, and that change of the signal is represented in the orbitofrontal cortex."

    One aspect that Professor Rolls was at pains to point out was that taste combines with a number of other senses and factors to determine how our brains react to a certain kind of food, and how pleasurable it is. These other factors can include preconceived ideas about certain foods, or the effect of a certain word being associated with a taste or smell.

    For example, the Professor suggested that the taste of umami can be made more pleasurable to the brain by bringing another sense into play, namely smell. In one experiment, people were given some umami taste and asked to give it a pleasantness rating. They were then given the same taste, but this time combined with a garlic smell. This combined taste and smell to form a flavour yielded higher pleasantness ratings, and thus, "part of the secret of cuisine is to get the correct odour lined up with the taste."

    One member of the audience was concerned that he might not be able to enjoy the umami taste to the full because he suffered from hypertension and was under doctor's orders to maintain a low-salt diet. Professor Rolls set his mind at rest by saying that, on the contrary, umami could actually be used to reduce salt intake, because it accentuates the savoury flavour present in dishes, so that less salt should be needed.

    Cheese or Body Odour?

    Another experiment recounted by the Professor dealt with the issue of cognition on the pleasantness of food, and in particular, "if you think something is a particular food, is that going to influence how it tastes to you?" In the experiment, people were exposed to a smell similar to that of brie cheese. Some people, however, were told that the smell was cheese, whilst others were told that it was body odour. As may have been expected, the pleasantness rating was higher when participants were told it was cheese and lower when they were told that it was body odour.

    What Professor Rolls found particularly exciting, however, was the fact that in the secondary smell and taste cortex of the brain there was much more activity when people were told the smell was cheese than when they were told it was body odour. Thus, the words themselves affected the extent to which the smell affected the brain, demonstrating the importance of cognition in the fundamental representation in the brain of the pleasantness of food. As the Professor underlined, "what we believe cognitively, even with language, can reach down to the first bit of the brain that represents emotion, or in this case how pleasant a savoury odour is."

    In this way, he concluded, it can be said that our enjoyment of food is affected by a combination of factors, which could be purely taste, or taste and smell, or even flavour and cognition.
    The Professor rounded off his talk by neatly encapsulating the difference between his role and that of, say, chefs by noting that, "we can unpack, as scientists, the rules that are involved in taste, but we rely on people like Heston Blumenthal (chef of The Fat Duck) and the other speakers here tonight to explain at the artistic level what particular combinations do good things."

    The Professor rounded off the evening with a comment on molecular gastronomy, and how this would develop in the future. He pointed out that 350 different types of human smell receptors have already been identified, and predicted that it would soon be possible to generate flavour molecules that can activate or block each of these, leading to an unprecedented level of control over the flavours in our food. Without doubt, a true glimpse of New Frontiers of Taste.

    We will be bringing you details of what these other speakers had to say in the following months, so be sure to subscribe to our Umami e-newsletter to keep up to date with all the latest articles on the website. (Subscribe our e-newsletter)

    Next month, you can read how Stefan Gates displayed a certain amount of scepticism about umami, and explored some of the myths and misconceptions that can build up around food.